In 2001, over 1.2 million new cases of human cancer will be diagnosed and over 0.5 million people will die from cancer (American Cancer Society estimate). Despite this, more people than ever are living with and surviving cancer. In 1997, for example, approximately 8.9 million living Americans had a history of cancer (National Cancer Institute estimate). People are more likely to survive cancer if the disease is diagnosed at an early stage of development, since treatment at that time is more likely to be successful. Early detection depends upon availability of high-quality methods. Such methods are also useful for determining patient prognosis, selecting therapy, monitoring response to therapy and selecting patients for additional therapy. Consequently, there is a need for cancer diagnostic methods that are specific, accurate, minimally invasive, technically simple and inexpensive.
Colorectal cancer (i.e., cancer of the colon or rectum) is one particularly important type of human cancer. Colorectal cancer is the second most common cause of cancer mortality in adult Americans (Landis, et al., 1999, CA Cancer J Clin, 49:8-31). Approximately 40% of individuals with colorectal cancer die. In 2001, it is estimated that there will be 135,400 new cases of colorectal cancer (98,200 cases of colon and 37,200 cases of rectal cancer) and 56,700 deaths (48,000 colon cancer and 8,800 rectal cancer deaths) from the disease (American Cancer Society). As with other cancers, these rates can be decreased by improved methods for diagnosis.
Although methods for detecting colorectal cancer exist, the methods are not ideal. Digital rectal exams (i.e., manual probing of rectum by a physician), for example, although relatively inexpensive, are unpleasant and can be inaccurate. Fecal occult blood testing (i.e., detection of blood in stool) is nonspecific because blood in the stool has multiple causes. Colonoscopy and sigmoidoscopy (i.e., direct examination of the colon with a flexible viewing instrument) are both uncomfortable for the patient and expensive. Double-contrast barium enema (i.e., taking X-rays of barium-filled colon) is also an expensive procedure, usually performed by a radiologist.
Additional methods for detecting colorectal cancer require tissue from the tumor. In order to use these methods, growth of the tumor must have progressed far enough that the tumor is visible. A second disadvantage of these methods is that they require a tissue biopsy to be taken from the tumor.
Because of the disadvantages of existing methods for detecting colorectal cancer, new methods are needed.